I happened to find a line in the source code where 50 was added to the score for linked monitors, but I had no Linked Monitors selected (and no other monitors were in the alarmed state anyway).
Just for the heck of it, I selected and then deselected my 3 other monitors in the Linked Monitors list, saved the configuration, and the problem was solved. Now my hard disk doesn't fill up after the first event.

I didn't examine the linked monitor list in the database, but I wonder if it had a bogus linked monitor listed. I am guessing that possibly deleting and recreating the problem monitor might have resolved the issue as well.
Anyway, my issue is solved, I'm just posting this hint in case anyone else runs into the same issue. Thanks!